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net/flow_dissector: switch to siphash

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UDP IPv6 packets auto flowlabels are using a 32bit secret
(static u32 hashrnd in net/core/flow_dissector.c) and
apply jhash() over fields known by the receivers.

Attackers can easily infer the 32bit secret and use this information
to identify a device and/or user, since this 32bit secret is only
set at boot time.

Really, using jhash() to generate cookies sent on the wire
is a serious security concern.

Trying to change the rol32(hash, 16) in ip6_make_flowlabel() would be
a dead end. Trying to periodically change the secret (like in sch_sfq.c)
could change paths taken in the network for long lived flows.

Let's switch to siphash, as we did in commit df453700e8
("inet: switch IP ID generator to siphash")

Using a cryptographically strong pseudo random function will solve this
privacy issue and more generally remove other weak points in the stack.

Packet schedulers using skb_get_hash_perturb() benefit from this change.

Fixes: b56774163f ("ipv6: Enable auto flow labels by default")
Fixes: 42240901f7 ("ipv6: Implement different admin modes for automatic flow labels")
Fixes: 67800f9b1f ("ipv6: Call skb_get_hash_flowi6 to get skb->hash in ip6_make_flowlabel")
Fixes: cb1ce2ef38 ("ipv6: Implement automatic flow label generation on transmit")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Jonathan Berger <jonathann1@walla.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Reported-by: Benny Pinkas <benny@pinkas.net>
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2019-10-22 07:57:46 -07:00 • committed by David S. Miller
parent 6c5d9c2a6b
commit 55667441c8
8 changed files with 42 additions and 43 deletions
Download patch file Download diff file Expand all files Collapse all files

4
include/net/fq_impl.h
View file

@ -108,7 +108,7 @@ begin:
static u32 fq_flow_idx(struct fq *fq, struct sk_buff *skb)
{
u32 hash = skb_get_hash_perturb(skb, fq->perturbation);
u32 hash = skb_get_hash_perturb(skb, &fq->perturbation);
return reciprocal_scale(hash, fq->flows_cnt);
}
@ -308,7 +308,7 @@ static int fq_init(struct fq *fq, int flows_cnt)
INIT_LIST_HEAD(&fq->backlogs);
spin_lock_init(&fq->lock);
fq->flows_cnt = max_t(u32, flows_cnt, 1);
fq->perturbation = prandom_u32();
get_random_bytes(&fq->perturbation, sizeof(fq->perturbation));
fq->quantum = 300;
fq->limit = 8192;
fq->memory_limit = 16 << 20; /* 16 MBytes */